The present invention relates to an on-line database management system for managing large-volume database transactions, and more particularly, to a database management technology for processing applications storing databases in a storage unit under the control of a SAN (Storage Area Network) and providing continuous around-the-clock services.
An on-line processing application handling large-volume transactions requires daily, weekly, monthly processing such as counting of large-volume data and batch registration, or periodical batch processing such as database backup and reorganization. Since these types of processing involve batch access to databases used for on-line services, these types of processing have great influences on processing of on-line processing applications, constituting an obstacle to around-the-clock service operations.
As a solution to this problem, a method of providing a plurality of database management systems on a LAN/WAN, transmitting updated contents of a database used for an on-line processing application to another database management system over a network at the appropriate times, reflecting them and replicating the on-line processing application database is known as described in JP-A-8-185346 and JP-A-2000-112801. By realizing the above-described batch processing with the database on the replicating side, it is possible to avoid concentration of load on the on-line processing application side and continue on-line services in parallel with batch processing.
A SAN (Storage Area Network) configuration, which organically connects a plurality of storage units such as magnetic disk units over a dedicated high-speed network, is becoming widespread in recent years. In this configuration, the storage units provide a function of speedily copying an arbitrary logical volume to a plurality of logical volumes, a function of multiple data writing using an arbitrary logical volume as a primary volume and a plurality of other logical volumes as secondary volumes, a function of separating logical volumes in a multiple write status at arbitrary timing and accessing them as primary and secondary volumes independent of one another, a difference reflection function of restarting multiple write using an arbitrary logical volume as a primary volume and a plurality of other logical volumes as secondary volumes and reflecting only differences between both data from the primary volume to the secondary volumes, etc. Furthermore, a plurality of CPUs connected on the SAN can perform input/output to/from an arbitrary storage product within the network as in the case where the CPUs and the storage product are directly connected.
Here, the “multiple data writing” means a process in which when an operation (insertion, update or deletion) is performed for certain data in a master database (i.e., a source database which creates a replicated database (or replica database)), the same operation is performed for data, which corresponds to the certain data, in the replicated database.
An application example of database access in this connection mode is a backup method described in JP-A-2000-347811. This system makes it possible to speedily copy a logical volume storing a database on the on-line processing application side to another logical volume and replicate the database, which in turn can be used as a backup in preparation for database trouble with the on-line processing application database.
On the other hand, the replicated databases created in this way are physical copies and accessing them as databases requires information for the database management system side to have access to the replicated databases. Therefore, this problem is handled by starting database management systems having the same database definition information as that on the on-line processing application side for their respective replicated databases separately (NIKKEI OPEN SYSTEMS, June 2001 (no.99) pp.266–267).